Variation in the acquisition and distribution of an organic nitrogen source by different genotypes and species of ectomycorrhizal fungi

Boreal forest soil is dominated by organic forms of nitrogen (N; approx. 90 – 95%), which are not immediately available for plant acquisition. The ensuing competition between plants for readily available inorganic N has resulted in the formation of mycorrhizas, a symbiotic relationship between a plant and fungus that colonises its roots. The fungus can acquire organic N forms from the soil, and transfer the N to the plant in return for other nutrients. Different species and genotypes of fungus have been found to differentially utilise organic compounds, which leads to inter- and intraspecific variation in the transfer of N and C to the host plant.
This research utilised monoculture and mixture microcosms containing Scots pine (Pinus sylvestrus) seedlings colonised with four species of mycorrhizal fungi (Lacarria bicolor, Suillus variegates, Paxillus involutus, Amanita rubescens) and four genotypes of L. bicolor (LbA, LbB, LbC, LbD), and Magenta boxes containing Scots pine seedlings colonised with two genotypes of L. bicolor. The colonised Scots pine seedlings were studied in monoculture and mixture microcosms to determine the impact inter- and intraspecific variation may have on N and C uptake and transport. The Magenta boxes had a separate middle compartment that excluded plant roots and was filled with three types of media in order to study the combined effects of intraspecific variation and fungal hyphal uptake of N and transport to the host shoots. Labelled (15N, 13C) glutamic acid was used as the N and C source. Isotope ratio mass spectrometry was used to determine the 15N and 13C shoot enrichment of the seedlings.
Results from the Magenta box experiment were inconclusive in determining the attraction of L. bicolor hyphae for specific types of middle compartment media, and the uptake and distribution of N derived from glutamic acid. Overall, the results from the microcosm experiments showed that seedlings associated only with genotype LbA had significantly different 15N shoot enrichment (p < 0.05), and seedlings associated with all four species of fungi had significantly different 13C shoot enrichment (p < 0.05). However, the Tukey post-hoc correlations showed that the four species did not differ from each other in 13C shoot content. This data suggested that there was intraspecific variation in the use of glutamic acid, but no interspecific variation.

This project was my MSc thesis at the University of Aberdeen (May - Sept 2014). I investigated the symbiotic relationship between ectomycorrhizal fungi and Scots pine seedlings, to classify the impact of species and genotypic variation on nutrient acquisition and transport within the fungi-plant system. An Isotope Ratio-Mass Spectrometry method was developed for analysis of isotopically-labelled amino acids in seedling roots and shoots. This research identified the positive impact specific fungal species have for promoting nutrient uptake in Scots Pine, and elucidated the possible long-term effects of ectomycorrhizal symbiosis for promoting forest restoration and ecosystem preservation. I received a first class mark, the highest grade, for this work. This research was included in a publication by Dr Christina Hazard http://www.genomenviron.org/People/Hazard/Hazard.html